A study was conducted to investigate the capacity of Tanzanian kaolin-feldspar blends on water defluoridation. Five adsorbents of kaolin-feldspar blends were prepared at different ratios, namely; 1:0, 1:1, 1:2, 2:1 and 0:1.The prepared adsorbents were activated at 60°C and then characterized by XRD and XRF. Mineralogical results showed that kaolin contained phases of kaolinite, illite and quartz whereas feldspar contained microcline and quartz. Chemical composition results indicated that both kaolin and feldspar samples contained silica and aluminium in high proportions. Defluoridation studies were conducted by using column method. Different parameters were tested for water defluoridation studies including particle size, contact time, initial fluoride ion concentration, height of the column and solution pH. It was observed that the adsorption increased with a decrease in particle size, and particle size of 0.25 mm showed the highest removal of fluoride. The fluoride adsorption was found to increase with contact time with optimum contact time after 45 minutes. A high adsorption of fluoride ions for all samples was observed at low pHs (2-6) and the maximum adsorption was at pH 2. Also the adsorption increased as the height of the column was increased. Regeneration of spent adsorbent did not afford to remove fluoride to acceptable levels, an aspect that needs more investigation. The study therefore concludes that, although the blends can be used as defluoridation materials; blending kaolin and feldspar did not improve adsorption of fluoride ions from fluoridated water. The best adsorbent was B1 which consists of kaolin only followed by B2 with 2:1 kaolin-feldspar ratio.

Bjorvatn, K and Bårdsen, A., Use of activated clay for defluoridation of water. Proceedings of the 1stInternational workshop on fluorosis and defluoridation of water, Ngurdoto, Tanzania. 1995, p. 49-55.